ephialtes

n.

nightmare or demon that causes nightmares, c.1600, from Greek Ephialtes, name of a demon supposed to cause nightmares; the ancient explanation is that it was from ephallesthai "to leap upon," but OED finds "considerable" phonological difficulties with this.

Ephialtes

leader of the radical democrats at Athens in the 460s, who by his reforms prepared the way for the final development of Athenian democracy. His hostility toward Sparta and his advocacy of power for the Athenian common people made him the enemy of the pro-Spartan politician Cimon, who had the support of the nobles. Elected general soon after 465, Ephialtes unsuccessfully opposed (462) the sending of an Athenian contingent under Cimon to assist in putting down a revolt of the helots in Sparta. The Spartans, however, dismissed the Athenian troops sent to relieve them. Outrage over the dismissal swung Athenian opinion in Ephialtes' favour, so that he was able in 462/461 to carry measures stripping the aristocratic court, the Areopagus, of its political power and to establish the dominance of the Ecclesia (the Popular Assembly), the Boule (Council), and law courts. Opposition to these measures resulted in the assassination of Ephialtes, but his political revolution was consolidated